It would be great to have internationally standardized pallet sizes in order to optimize the total capacity of a carrier, but the standards are far from universal. There are, however, several common sizes of pallets:
40” x 48” Similarly: 1000 mm x 1200 mm; these are most common across the world
42” x 42” Common in North America, Europe, and Asia
45.9” x 45.9” Common in Australia
43.3” x 43.3” Common in Asia